1. Field of the Invention
The present invention relates to an image forming apparatus for forming a test image on paper and adjusting the density correction characteristic in the printing on the basis of the measured density of the test image.
2. Description of Related Art
In an image forming apparatus, the density correction is carried out as one correction for correcting the process conditions in the printing. As a method for preparing or adjusting the density correction characteristic (in general, referred to as “printer gamma characteristic”) used in the density correction, there is a method in which a patch of a test image is formed on paper and the density correction characteristic is prepared or adjusted on the basis of the result of the density measured by a density sensor. The above method is referred to as the output paper density adjustment.
The output paper density adjustment has the important feature that the printer gamma which is optimized for the paper used in the printing is prepared. Because it is necessary to adjust the density by using the paper which is actually used in the printing, the output paper density adjustment is carried out by feeding the paper from the tray used in the printing. The adjustment timing of the output paper density adjustment is the timing at which the change of the process conditions, such as the temperature, the humidity and the like, exceeds the predetermined threshold value (in general, the timing at which image stabilization control is started). Further, because some users hate the characteristic change associated with the time degradation of the device, the device has also the periodic adjustment function in which the output paper density adjustment is carried out, for example, every 1000 [sheets/print].
In case that the paper having the size (for example, the postcard size) which is less than the minimum size in which the density can be detected by using a color measurement sensor used in the output paper density adjustment is used, the patch data cannot be printed on the sensor line. As a result, the output print density adjustment cannot be carried out, and it was required to apply a general IDC sensor type of printer gamma.
Further, in case that the paper to be used in the print job is patterned special paper, the paper on which the serial number is printed or the paper in which a pattern is printed on the center line, some users have the request in which the density is adjusted by using the same type of the plain paper set to a different tray. In this case, the output paper density adjustment is carried out at a high accuracy as compared with the conventional one. On the other hand, the paper used in the output paper density adjustment is wasted.
Therefore, the method in which the paper used in the output paper density adjustment is fed from a feed tray different from the feed tray for feeding the paper used in a print job, has been proposed. For example, the following image forming apparatus has been proposed. In this image forming apparatus, the feed tray in which the suitable paper for the output paper density adjustment is contained is automatically searched, and the output paper density adjustment is carried out by feeding the paper from the searched feed tray (See Japanese Patent Application Publication No. 2008-287017).
In case that the output paper density adjustment is carried out during the execution of the print job by feeding the paper from the substitute feed tray, it is required to use the paper in which the output paper density adjustment can be carried out under the same conditions as the paper used in the print job, even though the size and the weight of the paper are different or the special paper is used in the print job.
On the other hand, in the output paper density adjustment, because it is required that the process conditions which are used in the printing of the patch on the paper and the correction characteristic of the density sensor are constant according to each type of the paper, the information relating to the process conditions and the like, is generally obtained by referring part of the paper related information registered so as to relate it to the feed tray for feeding the paper used in the output paper density adjustment.
Therefore, in order to carryout the output paper density adjustment by feeding the paper from the substitute feed tray, it is required to set the paper of the same type as the paper used in the print job and having the suitable size, to the substitute feed tray, and to change at least the information referred in the output paper density adjustment among the paper related information set to the substitute feed tray, to the values set to the feed tray for feeding the paper used in the print job. Further, after the output paper density adjustment is finished, it is required that the above changed information returns to the original information. There is a problem that the burden for the above change of the information is large and the mistake in the above change is easily caused. Therefore, due to the above problem, the productivity and the quality in the printing were lowered and the running cost of the printing was increased.